In the semiconductor's manufacturing, hundreds of processing steps are needed for a semiconductor device. A product travels through different types of stages in a processing line, and a product has different processing time in every stage. For example, diffusion stage and implanting stage have long processing time (4-12 hours). The long-time stages are the bottlenecks of the processing line in a FAB. Also, a specified amount of wafers are put into the processing line everyday, but the processing speed of these wafers will be slow down in these long-time stages. When the tool's capacities of the processing line is reduced, the throughput of the processing line is reduced, too. The above condition reduces the efficiency of the machines in the FAB and increases the cost of the production in the semiconductor manufacturing. Thus, the goal to perform continuous production is important, and performing the dispatching is a great challenge in order to make sure the stability of the throughput of the processing line.
To make sure the production running continuously within finite tools, controlling the number of wafer-in-process (WIP) and the number of wafers to be put in the processing is important. In the prior art, using the key-stage report (KSR) of a processing line is a usual method to understand the working condition of the machines in the processing line. In the KSR, several parameters of the processing line are recorded. These parameters include the quantities of wafers which are in the preprocess of a stage, in the process of a stage and at the end of a stage.